What is the role of posterior spinal fusion and segmental instrumentation in the treatment of spinal muscle atrophy (SMA)?

Updated: Aug 11, 2020
  • Author: Ashish S Ranade, MBBS, MS, MRCS; Chief Editor: Jeffrey A Goldstein, MD  more...
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The most common orthopedic problem is scoliosis, which is often severe. [58]  It is universal among nonambulatory patients, in whom the curve progression is about 8° annually, despite brace treatment. Half of ambulatory patients develop scoliosis as well, but at a slower rate of progression.

In a cohort of 238 SMA patients, it was found that the lifetime probability of scoliosis surgery was high in types IC and II and was dependent on age at the loss of ambulation in type III. [59]

Posterior spinal fusion with segmental instrumentation is indicated in young patients whose curve cannot be controlled with a brace and in patients older than 10 years with curves greater than 40° and forced vital capacities 40% above normal. The entire thoracic and lumbar spine down to the pelvis should be fused to obtain a balanced trunk and a leveled pelvis. As a rule, concomitant anterior spinal fusion to prevent crankshaft phenomenon is avoided; the risk of potential problems with anterior spinal surgery in a patient with SMA outweighs the benefits.

In ambulatory patients, spinal surgery that excludes the pelvis is preferred. Compensatory lumbar lordosis and pelvic motion have been observed to compensate for the proximal motor weakness in these patients. The ambulatory capacity of some of these patients may be lost after surgery.

Surgery should be delayed as long as medically possible. It should be kept in mind that curve progression is slower in patients with type III SMA and that these patients present later in life. However, when surgery is necessary, it should be performed while the patient is still ambulatory. This is in contrast to the preferred timing for surgery in patients with Duchenne muscular dystrophy. (See the images below.)

Spinal muscle atrophy. Immediate postoperative ant Spinal muscle atrophy. Immediate postoperative anteroposterior radiograph of patient at age 9 years. Thoracic curve is now at 18°, and lumbar curve is 35°, which represents more than 67% curvature correction.
Spinal muscle atrophy. Immediate postoperative lat Spinal muscle atrophy. Immediate postoperative lateral view with good sagittal balance.

Scoliosis correction in children younger than 10 years remains a challenge. Various growing systems (eg, growing rods and the vertical expandable prosthetic titanium rib [VEPTR]) have been used. [60, 61, 62]  

In a study by Chua et al, scoliosis correction was shown to have a beneficial effect on pulmonary function at a mean follow-up of 11.6 years. [63]  Before surgery, the rate of decline of the predicted forced vital capacity was 5.31% per year; after surgery, it was reduced to 1.77% per year. In another study, at 10-year follow-up, posterior spinal fusion was found to be effective in controlling curve progression and pelvic obliquity without negatively impacting the space available for lung, trunk height, and pulmonary function. [64]

The role of growth-friendly spine surgery in SMA is evolving. A study by Lenhart et al demonstrated stabilization of respiratory support requirement following the insertion and lengthening of posterior-based growing rods. [65]  

In a study of 28 SMA patients, it was found that the results of definitive spinal fusion were better in children with prior growth-friendly surgery than in untreated patients. [66]

In another study, it was found that prophylactic fusion with implant revision was not necessary in nonambulatory children with SMA, and the growing rods were maintained. [67]

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